The manufacture of tobacco smoke filters from a continuous multifilament filter tow generally involves processing steps which include separation of the individual filaments (i.e., "opening up" of the filter tow), the application of plasticizer and other additives to the "opened up" tow and the formation of a continuous filter rod from the treated filter tow. The uniformity and filtering characteristics of the resulting filter rod are largely determined by the effectiveness of these tow processing steps. The processing steps become particularly critical when the applied additives include flavoring materials or other active agents which modify the tobacco smoke as it passes through the filter.
U.S. Pat. No. 2,966,198 discloses apparatus for applying aqueous solutions of cellulose derivatives to filter tow as the tow is subjected to a turbulent current of air. Although this apparatus may be suitable for applying solutions of film-forming binders to the tow, it does not provide the degree of control required for producing a uniform filter rod.
The application of various flavoring materials to tobacco smoke filters is disclosed in U.S. Pat. No. 3,144,024 but apparatus for incorporating such materials is not specifically described.
U.S. Pat. Nos. 3,371,000 and 3,847,064 disclose methods and apparatus for making tobacco smoke filters containing added filtration materials such as activated carbon. Various apparatus designs are described which inject a slurry of activated carbon into the filter tow at spaced intervals. Closely related to these patents are U.S. Pat. Nos. 3,095,343 and 3,774,508 which describe methods and apparatus for shaping filter tow into a hollow cylindrical rod by positioning a mandrel concentrically in the path of the moving filter tow and injecting steam into the filter tow.
In U.S. Pat. Nos. 3,779,787 and 3,853,039 an additive is introduced into a filter rod by piercing the rod with a needle and submerging the pierced rod in a liquid additive bath or, alternatively, by directing a jet of liquid additive against the rod with sufficient force to impregnate the filter rod.
Another method for incorporating additives into tobacco smoke filters is disclosed in U.S. Pat. No. 4,281,671 and involves combining filter tow and a thread impregnated with a smoke-modifying agent in the manufacture of a tobacco smoke filter. The surface area presented by the impregnated thread is quite limited, however, and the portion of tobacco smoke contacting the thread is also correspondingly quite limited.
A dual filter construction is disclosed in U.S. Pat. No. 3,313,306 which is formed from a fibrous filter tow that may optionally be treated with additives. The filter tow is formed into an elongated rod which is compressed at spaced locations to give a compacted core of tow that is provided with an annular sheath of a second filter material such as carbon granules at the spaced locations.
U.S. Pat. No. 4,291,711 discloses a filter formed from reconstituted tobacco and a fibrous filter tow with either material constituting a central longitudinal core that is enveloped by an annular sheath of the other material. The reconstituted tobacco may optionally be treated with tobacco flavorants.
The manufacture of filter rods from continuous multifilament filter tow typically involves moving the filter tow in a generally longitudinal direction through a succession of treatment steps designed to align and spread apart the individual filaments by mechanical and/or pneumatic means so that plasticizers and other additives may be applied to the aligned and spread filter tow before the tow is gathered and formed into a predetermined shape such as a substantially cylindrical rod. The processing steps may also include the application of paper wrap to the filter tow to produce a paper wrapped filter rod. When the manufacture of filter rods also involves incorporation of flavoring materials, the application of flavoring materials to the filter tow has heretofore generally involved dissolving such materials in the plasticizer. Such a method of application, however, does not provide a very precise degree of control over the levels of flavoring materials applied to the filter tow and it also results in contamination of the apparatus used for applying plasticizer. The contamination problem is particularly objectionable when filter rods containing different flavoring materials are to be produced using the same apparatus.
Current commercial manufacture of filter rods from filter tow involves two basic techniques for pretreatment of the tow prior to formation of the filter rod. One technique uses pneumatic banding jets and cooperating sets of rolls including circumferentially grooved rolls adapted to contact and to spread and stretch the filter tow thereby transforming the tow into a flat wide band that is then passed through a chamber where plasticizer is applied to the band of tow by spray or other suitable means. The other technique employs a pneumatic banding jet to create a narrow flat band of tow that is drawn across wick-type applicators which deposit plasticizer on both sides of the band of tow before the tow is passed through a jet device for stretching, aligning and blooming the tow. In both techniques the pretreated filter tow, comprising a longitudinally oriented assemblage of filaments having individual filaments of the tow in substantial alignment, is fed into a converging horn or funnel located adjacent to the entrance of filter rod-forming means. The converging horn or funnel gathers and compresses the filter tow into a rounded, rope-like configuration and a tongue device located between the converging funnel and rod-forming means applies further converging and compressing forces to the filter tow as the tow enters the garniture of the rod-forming means. The rod-forming means may be provided with means for heating the advancing filter tow sufficiently to produce a stable, continuous non-wrapped filter rod or it may be provided with means for wrapping the filter tow in a continuous paper web to produce a continuous paper-wrapped filter rod. In some commercial filter rod-forming operations, a stuffer jet or transport jet is utilized as converging means for gathering the flat band of treated filter tow and transforming it into a loosely compacted rope-like configuration that is directed to the rod-forming means. The stuffer jet or transport jet is usually located adjacent the entrance to the rod-forming means. Stuffer jets or transport jets typically comprise a truncated cone-shaped device having a large end for receiving the advancing filter tow and a small end for discharging the filter tow with orifice means intermediate the large end and small end for directing a pressurized gaseous medium onto the advancing filter tow.